Developement of the non-invasive deep-body temperature measuring method by reflected Ultrasouna

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Present uses of thermocouple and thermistor in measuring body temperature face many problems. For example, the problem of limited number of measured points and metastasis in hyperthermia thermometry. These problems necessitate non-invasive temperature measurement. When ultrasound propagated through biological material, its physical parameters such as attenuation and velocity vary with temperafure. Among these parameters, attenuation seems the most practical since the existing B-mode device can be used to analyze the attenuation of reflected ultrasonic signal. The purpose of this study is to show the possibility of non-invasive temperature measurement method based on the above principle.In biological tissuse, structural relaxation processes, with an appropriate distribution of relaxation times and the contribution due to viscosity, give rise to the measured attenuation coefficient. Because viscosity and relaxation processes are related to the temperature through viscosity coefficient and relaxation times at different temperature, respectively, the attenuation coefficient is a function of temperature. Consequently, the temperature will be measured indirectly by estimating attenuation coefficient parameter.For basic study, the in vitro experiments using pig livers, pig fillets, beef livers and beef muscles were investigated. The technique used to analyze the temperature dependence of attenuation cofficient is the spectral-difference method. The experimental results indicate that the temperature dependences of attenuation coefficients of liver and muscle in the temperature range of 37-46゜C are in the order of -.006 to -.011 dB/(cm.MHz.K). In vivo experiment using pig liver also shows the negative dependency. By a more accurate instrumentation and signal processing, with preliminary known characteristics of the temperature dependences of attenuation coefficients of the tissuse of interest, it is possible to measure the tissue temperature non-invasively by this method.